The Author(s) 2018. This article is published with open access at www.chitkara.edu.in/publications.

ABSTRACT

Polymer films of styrene butadiene copolymer (SBC) mixed with SiO2:Ge powder were successfully obtained by the drop casting method. The SBC concentration (in chloroform solution) was 10%w/v and the SiO2:Ge powder was mixed (mass ratio 80:20 respectively). The thicknesses of the films obtained were 50, 100, and 200 μm. In addition, polymer films of polytetrafluoroethylene (PTFE) preparation (60% dispersion in water), were obtained mixing 2 ml of PTFE and 0.05g of SiO2:Ge powder with a mass relation of 98% polymer and 2% SiO2:Ge. The photoluminescence emission spectra (PL) of SBC doped with SiO2:Ge resulted in similar characteristics to those for SiO2:Ge powders, although their intensity shows an increase 3.5 times approximately, compared with the pure powder. On the other hand, the PTFE films with SiO2:Ge present just one peak in the PL emission at 439 nm but their intensity increases 18 times respect to the powder. The photoluminescence excitation (PLE) spectra of the SiO2:Ge powders show the characteristic peaks at 248 nm (most intense) and at 366 nm. However, when the powder is embedded either in SBC or PTFE the peak at 366 nm shows an important increase which seems to indicate an energy transfer from the polymer to the SiO2:Ge..

INTRODUCTION

In the last decade the research in films of SiO2 doped with germanium has increased, due to their potential applications in optoelectronics and solar cells [1,2]. However, it is necessary to improve the photoluminescence (PL) properties to make them more attractive for these applications. For that reason, some research groups have implemented strategies as thermal treatments [3], the confinement of Ge in a sandwiched structure [4] or use a polymer as a matrix to improve their PL properties. In this work, SiO2:Ge powders were embedded in two different polymers, the first was styrene butadiene copolymer (SBC) whose transmittance characteristics are very interesting for optoelectronic applications, obtaining an improvement in the PL intensity. On the other hand, the polymer films with PTFE shows an enhancement in the PL intensity of around 18 times.

Thin films of SiO2:Ge powders embedded in two polymeric matrices were successively obtained. The polymers are (a) styrene butadiene copolymer (SBC) and (b) polytetrafluoroethylene (PTFE). The obtained films have thermal stability up to 370°C for the first one and up 550°C for the other, respectively. The photoluminescence properties of both polymeric structures were enhanced by an efficient energy transfer between the SBC and PTFE polymers to SiO2:Ge powders. This is validated by the overlap of the PL excitation spectra of SiO2:Ge powders with the polymer PL emission spectra. The PL spectra are associated with the color centers of germanium that are present as it can be observed in the FTIR spectra by the vibrations at 460, 796, 1020, and 1080 cm–1.